Natural oil-derived polyols have been considered as alternatives for petroleum-based polyols for use in the polyurethane industry for making polyurethane materials. For making polyurethane materials, proton-activated groups, such as hydroxyl groups, are necessary for the reactions with isocyanate groups that result in urethane linkages. Almost all of the commodity vegetable oils, except for castor oil, unfortunately, contain no hydroxyl groups in their triacylglycerol structures of saturated and unsaturated fatty acids. However, the supply of castor oil is restricted because of its growth in limited geographical areas.
There is a need to chemically introduce hydroxyl groups onto the triacylglycerols of the vegetable oils for the uses in the polyurethane industry.
Polyurethanes are a class of polymeric materials with a wide spectrum of properties that make these materials of great use to the daily life of mankind. For example, polyurethanes are used in furniture, clothing, automotive, carpets, and many more applications in the form of foams, elastomers, coatings, adhesives, sealants, and composites.
In the U.S. patent application Ser. No. 10/924,332, filed on Aug. 23, 2004, Casper et al. claimed a simple, economic process to produce polyols from vegetable oils. The process is a “one-pot” process using acetic acid and hydrogen peroxide to oxidize the double bonds of the unsaturated fatty acids of the triacylglycerol structures thereby forming an epoxy group, and then conducting ring-opening of these epoxy groups in situ with acetic acid at an elevated temperature. The ring opening of an epoxy group with acetic acid generates a hydroxyl group and an adjacent acetate group simultaneously at the C9, C12, or C15 sites of C18-C22 fatty acid carbon chains. Because the hydroxyl groups are generated near the middle of the fatty acid chains, such hydroxyl groups are secondary hydroxyl groups.
No additional catalyst was needed in this process. No inorganic acids were used in this process as well. The final polyols produced from this process are composed of triacyl-glycerol structures as the basic units but somehow a portion of them can be linked together so that these dimer or higher oligomerized triacylglycerol units result in giving an average molecular weight of the polyols that is about twice as high as that compared with the unhydroxylated initial triacylglycerols.
In the triacylglycerol units of the polyols produced from this process, functional groups such as hydroxyl groups, acetate groups, and carbon-carbon double bonds exist in the final structural units. The physicochemical characteristics of the polyols produced from the above mentioned patent application are: hydroxyl numbers of 69-195 mg KOH/g, viscosity of 119-35000 cP at 25° C., Iodine numbers of 5-15 cgI2/g, molecular weight of 1600-2200 Daltons, water solubility less than 0.004 percent weight/weight, freezing point 1-8° C., an acid number less than 1.0 mg KOH/g, a hydroxyl functionality from 2 to 7, no residual peroxides, and without inorganic acids. The molecular weight therein is a number-average molecular weight measured with GPC using narrow molecular weight distribution polystyrenes as standards. The existence of molecular weight distribution is inherent in the natural oil origin. Polyols that are synthesized from this patent-pending process are typically natural oil polyols and they are commercially available, under the brand name Agrol®, from BioBased Technologies, LLC, Rogers, Ark.
Monteavaro et al. in Monteavaro, L. L.; da Silva, E. O.; Costa, A. P. O.; Samios, D.; Gerbase, A. E.; Petzhold, C. “Polyurethane Networks from Formiated Soy Polyols: Synthesis and Mechanical Characterization. JAOCS (2005), 82: 365-371. (2005), prepared soy polyols with a one-step synthesis using formic acid and hydrogen peroxide on the double bonds of the vegetable oils (3/1.5/1).
This method followed the reaction steps of epoxidation of unsaturated fatty acids followed by ring-opening of the epoxy groups to form polyols. By simply varying the reaction time at 65° C., the polyols that were formed had hydroxyl numbers that ranged from 53-162, acid numbers of 1.2-2.2 and viscosities in the range of 230-9844 cP. Molecular weights of the polyols were reported up to 2404 Daltons. Based on the description in this publication, the structure of the resultant polyol is in the category of hydroxylated vegetable oil esters; however, the process forms a formic acid ester which is different than the acetic esters formed in the process of patent application Ser. No. 10/924,332 A1 mentioned Supra.
U.S. patent application 2007/0123725 A1 describes a process for the preparation of polyols based on natural oils converting unmodified unsaturated fatty acid triglycerides into polyols with peroxycarboxylic acids wherein phosphoric acid is used as a catalyst and followed by an additional alkoxylation step. In the step of preparing natural oil polyols and any further steps to modify the described natural oil polyols, no amines or hydroxyalkylamines were used in this patent application to form natural oil hydroxylates.
Fornol et. al. in Fornol, A. R.; Onah, E.; Ghosh, S.; Frazier, C. E.; Sohn, S.; Wilkes, G. L.; and Long, T. E., Synthesis and Characterization on Triglyceride-Based polyols and Tack-Free Coatings Via The Air Oxidation of Soy Oil. J. Appl. Poly. Sci. (2006), 102:690-697, applied dry-air oxidization on soybean oil to make polyols with hydroxyl numbers ranging from 7 to 110 mg KOH/g. Dry-air processes generated hydroxyl groups through the reactivity of adjacent protons of the double bonds on the unsaturated fatty acids. This can lead to natural oil polyols produced without additional ester formation.
U.S. Patent publication 2002/0058774 in the name of Thomas Kurth, et al describes a method to produce vegetable oil polyols in a transesterification process from a vegetable oil polyol with a multifunctional alcohol to form a polyol with selectable functionality.
WO Publication 2006/094227 A2 and U.S. Patent publication 2007/0173632 describes a method using an iron-containing catalyst in an oxidation process to produce natural oil-derived polyols having an increased hydroxyl number in which the hydroxyl number was as high as 220 mg KOH/g.
Guo and Petrovic et al. described in Guo, A.; Javni, I; Petrovic, Z., Rigid Polyurethane Foams Based on Soybean Oil. J. Appl. Poly. Sci. (2000), 77:467-473 the preparation of soy polyols via the oxirane/epoxide ring-opening reaction of epoxidized soybean oil with methanol. Methanol attacks the epoxy ring to generate a hydroxyl group and simultaneously form an adjacent ether bond on the fatty acid carbon chain. Therefore, such polyols are classified as hydroxylated vegetable oil ethers. The polyols had hydroxyl numbers ranging from 184-215 mg KOH/g and a viscosity ranging from 7200 to 10400 cP at ambient.
In another method, Zlatanic et al. in Zlatanic, A.; Lava, C.; Zhang, W.; Petrovic, Z. S. Effect of Structure on Properties of Polyols and Polyurethanes Based on Different Vegetable Oils, J. Poly. Sci.: Part B: Polymer Physics (2004), 42: 809-819, synthesized several polyols with epoxidation of the unsaturated fatty acid of oils followed by ring-opening of the epoxy groups in boiling methanol in the presence of tetrafluoroboric acid catalyst. The new oils were derived from canola, sunflower, soybean, linseed, sunflower, and corn oil. The hydroxyl numbers were determined to be 173.6 to 247.8 with a viscosity range of 1850-18200 cP at 27° C. In U.S. Pat. No. 6,107,433, Petrovic, et al. prepared vegetable oil-based polyols by adding a peroxyacid to a vegetable oil to give epoxidized vegetable oils and then this epoxidized vegetable oil was added to a mixture of an alcohol, water, and a catalytic amount of fluoroboric acid so as to form a vegetable oil-based polyol. The polyols prepared from this method had hydroxyl numbers ranging from 110-213 mg KOH/g and a viscosity ranging from 1000 to 7000 cP at room temperature. The above methods are multi-step processes. The polyols synthesized from the ring-opening with alcohols are hydroxylated vegetable oil ethers, which are different than hydroxylated vegetable esters in chemical composition.
Guo and Petrovic et al. in Guo, A.; Demydov, D.; Zhang, W.; Petrovic, Z. S. Polyols and Polyurethanes From Hydroformylation of Soybean Oil, J. Polym. Environment (2002), 10 (112): 49-52, utilized rhodium-catalyzed hydroformylation to synthesize two polyols with hydroxyl number of at 160 and 230 mg KOH/g. Hydroformylation generates a hydroxymethyl group adjacent to the carbon-carbon double bonds of the unsaturated fatty acids without generation of either additional ester or ether bonds, and thus the structure of the resultant polyol is different from either hydroxylated vegetable oil esters or hydroxylated vegetable oil ethers. Vegetable oil-derived polyols prepared from this hydroformylation method is also described in US 2006/0276609 A1. This is a multiple-step process because methyl ester formation, hydroxyformylation, and then use of the methyl ester to react with polyol, polyamine, or aminoalcohol are conducted as separated steps. In this process, amines were used to react with hydroxymethylated-fatty acid methyl esters (monomer). The reacting site for amine reactants is the methyl ester of the monomer in this patented process. One major disadvantage of this process is the generated methanol needs to be removed from the final product for polyurethane applications.
In U.S. patent application US 20060194974 A1, Narayan et. al. prepared polyols by the reaction of vegetable oil with ozone in a reaction mixture of alcohols and alkaline catalysts to cleave double bonds in fatty acid groups of the triglyceride. The polyols had 0.5-5.0 hydroxyl groups per triglyceride units as they claimed. However, no viscosity data was reported.
The synthesis of soybean oil-derived polyols from an ozone-mediated process has been disclosed by Tran et al in Tran, P.; Graiver, D.; Narayan, R. Ozone-Mediated Polyol Synthesis From Soybean Oil. Journal of the American Oil Chemists' Society (2005), 82(9), 653-719.
Petrovic et al. in Petrovic, Z. S.; Zhang, W.; Javni, I. Structure and Properties of Polyurethanes Prepared From Triglyceride Polyols by Ozonolysis, Biomacromolecules (2005), 6: 713-719, prepared soy polyols by ozonolysis from three oils. The hydroxyl numbers for trilinolein canola oil, soybean oil, and canola oil were 298, 228, and 260 mg KOH/g, respectively. The three polyols were solids at ambient temperature. Ozonolysis cleaves the unsaturated fatty acids to give shorter unsaturated fatty acids and therefore, vegetable oil-derived polyols prepared from ozonolysis compose triacylglycerols with lower molecular weights than the regular triacylglycerols in vegetable oils. In addition to the difference in the molecular weight, hydroxyl groups prepared from the ozonolysis are located at the ends of the fatty acid carbon chains thereby making them primary hydroxyls, whereas the hydroxyl groups prepared from the ring opening of epoxy groups, such as using the process described in the U.S. patent application Ser. No. 10/924,332, are located almost always at the C9 or C10, C12 or C13, and/or C15 or C16 carbon of the fatty acid carbon chains.
Kurth et al. claimed in the US patent applications U.S. 2003/0191274 and 2004/0209971 A1 that the functionality of blown soy oil was increased when glycerin was transesterified by the use of specific saccharides, for example, sucrose. The process described in these two patent applications is based on oxidation without using amines and/or hydroxyalkylamines.
Dwan'Isa et al. in WO 2004/099227 A2, Jena-pierre, L. Dwan'Isa, Lawrence T. Drzal, Amar K. Mohanty, Manjusri Misra, (Michigan State Univ. 2004), Polyol Fatty Acid Polyesters Process and Polyurethanes Therefrom, describe a solvent-free process for making a polyol fatty acid polyester compositions useful for the preparation of polyurethanes. These compositions were preferably made by reaction of natural oil with a multi-functional hydroxyl compound derived from a natural source, such as sorbitol, in the presence of an alkali metal salt or base such as potassium hydroxide. The latter compound serves as a catalyst which also acts to saponify the reaction mixture. The hydroxyl numbers of the polyols that could be obtained were as high as 434 mg KOH/g. The process described in this patent application is a transesterification process in nature. Similar processes can also be seen in the US patent application US 2002/0058774. In these patent documents viscosity values of the polyols were not given.
Wolff et al. in GB 1248919, (1968), describe Polyurethanes derived from fatty acid derivatives and also describe a method in GB 1248919A to prepare polyols from the reaction of a fatty acid or fatty acid methyl ester with diethanolamine, in which the hydroxyl numbers of the polyols are below 200 mg KOH/g. Viscosity values of these polyols were not reported. At least 80% of alcohols formed from the reaction were removed as described in one claim of the patented method.
Badri et al. in Production of a High-Functionality RBD Palm Kernel Oil-Based Polyester Polyol, Journal of Applied Polymer Science., Badri, K. H.; Ahmad, S. H.; Zakaria, S. (2001), 81(2), 384-389, synthesized refined, bleached, and de-odorized palm kernel oil-derived polyol by reaction of the oil with sorbitol and ethanolamine (70/30 ratio) with potassium octanoate as catalyst and ethylene glycol as emulsifier. The polyol was obtained with a viscosity of 1313 cP at 25° C. and the hydroxyl number ranged from 450-470 mg KOH/g. This process directly used the oil as the raw material, therefore, there are no hydroxyl groups initially present on the carbon chains of the fatty acids. A process, similar to Badri's method, but using soybean oil, is described in the Chinese patent application CN 1869184A. Again, there were initially no hydroxyl groups present on the carbon chains of the fatty acids.
Jenkines describes in WO 2005123798 a method of making carpet backings using fatty acid amide polyols. The inventor therein demonstrated that fatty acid amide polyols allow a significant replacement of conventional polyols with polyols derived from annually renewable resources, while maintaining important properties like edge curl, tuft bind, viscosity, and curing rates. The inventor mentioned GB 1248919 as supporting literature for the synthesis of the fatty acid amide polyols. In his description, the fatty acid esters used for preparing said fatty acid amide polyols can be obtained in a transesterification reaction between the oil or fat and a lower alcohol such as methanol or ethanol.
From his description, the resulting amide polyol typically contains a hydrocarbon tail corresponding to the initial fatty acid starting material (no hydroxyl group), and hydroxyl groups having a spatial relationship to each other that is defined by the structure of the starting alkanolamine compound. The hydroxyl equivalent weight is generally in the range of 125-225, preferably about 150-200. The fatty acid amide polyols used in the patent application WO 2005123798 are commercially available products from Ele & Pelron Corp., Lyons, Ill., having trade names PEL-AMID 676A (hydroxyl number 168 mg KOH/g), PEL-AMID 676 (hydroxyl number 110 mg KOH/g), and PEL-SOY744 (hydroxyl number 440 mg KOH/g). PEL-AMID 676A and 676 are ethoxylated products. PEL-SOY744 has a high hydroxyl number of 440 because it is blended with approximately 10% of glycerine.
Chinese patent application CN 1837180A describes a method of making biobased polyol from rapeseed oil. The first step of this method is an alcoholysis reaction with multiple alcohol and rapeseed oil with alkali hydroxides as catalysts to form mono-fatty acid esters. Epoxidation is then conducted on the alcoholyzed unsaturated fatty acids with organic peroxides. The third step is the ring-opening of the epoxy groups with proton-activated compounds including amines and ethanolamines. Water washing and purification steps are also used between or after each reaction step and prior to each reaction step to get a final polyol product. This is obviously a multiple step process. Amines and ethanolamines are used herein in the third step to open the epoxy rings formed on the unsaturated fatty acid mono-esters. The most preferred ethanolamines are those with tertiary amines such as triisopropanolamine, triethanol-amine, methyl diethanolamine, and methyl diisopropanolamine as disclosed.
CN 1837181A describes a method of making biobased polyol from rapeseed oil, in which the method promotes the epoxidation of rapeseed oil with organic peroxides, ring-opening of epoxy groups with alcohols, and then alcoholysis with multiple alcohols including ethanolamines. The use of water washing and purification steps are utilized after each reaction step and prior to each reaction step to obtain the final polyol product. The most preferred ethanolamines are those with tertiary amines such as triisopropanolamine, triethanolamine, methyl diethanolamine, and methyl diisopropanolamine as disclosed. In this complicated process, hydroxyl numbers of the final polyols can be higher than 500 mg KOH/g.
Hu et al. in Hu, Y.-H.; Gao, Y.; Wang, D.-N.; Hu, C.-P.; Zu, S.; Vanoverloop, L.; Randall, D. Rigid Polyurethane Foam Prepared From a Rapeseed Oil Based Polyol, Journal of Applied Polymer Science (2002), 84(3), 591-597, reported a two-step method to synthesize polyols from rapeseed oil. In the first step, rapeseed oil was reacted with hydrogen peroxide and formic acid at 40° C.-50° C. for 1 hr and then was allowed to stand overnight for the separation of water and oil phases. The hydroxylated rape seed oil was formed with a hydroxyl number 100 mg KOH/g, acid number 5 mg KOH/g, and viscosity of 400 cP at 25° C. Then the hydroxylated rapeseed oil was reacted with triethanolamine using Lithium hydroxide as catalyst at 150° C. The authors declared this was an alcoholysis process of the hydroxylated rapeseed oil with triethanolamine to produce a polyol of hydroxyl number 367 mg KOH/g, acid number 0.14 mg KOH/g, and viscosity 1600 cP. The reaction of hydroxylated rapeseed oil with ethanolamine and diethanolamine is also demonstrated as a side reaction, which is due to the ethanolamine and diethanolamine existing in triethanolamine as impurities.
In brief, the polyols described in the above published literature normally have hydroxyl numbers lower than 250 mg KOH/g and a few have hydroxyl numbers higher than 200 mg KOH/g. The hydroxyl number is one of the key parameters that impacts the property of polyurethane materials made with such polyols. Viscosity is another parameter that can also have greater impact on the processing and production effectiveness and the mixing quality in the preparation of polyurethane materials. For example, it would be favorable to use polyols in a spray process or a reaction injection molding (RIM) process or high pressure molded foam process. Therefore, there is a need to synthesize polyols having a high hydroxyl number and at the same time offering relatively low viscosity in the range of 100-10,000 cP at 25° C. In the preparation of vegetable oil-derived polyols via epoxidation reaction of double bonds, the hydroxyl number relates to the consumption of double bonds in the unsaturated fatty acid chains and it is normally difficult to obtain a vegetable-oil-derived polyol with a hydroxyl number higher than 250 mg KOH/g. On the other hand, one generally finds that higher hydroxyl containing polyols also give a higher viscosity. It is a challenge to synthesize vegetable oil-derived polyols with high hydroxyl number and low viscosity.